Immediate Mode Terminal UI

Experiments with immediate mode rendering for emulated terminals.

Originally started as a port of the reference">bearlibterminal api for webgl, which became a slightly simpler model, but with a full immediate mode rendering library too.

Eventually ripped out the rendering terminal rendering layer as termgl—a more general purpose way to render bitmap fonts to a console in a browser.

There’s a continuation of this work in termgl/ui that started with a better model for processing events, but the examples/demos here are more complete. This codebase also supports a canvas renderer, whereas termgl only works with webgl.